Chlorosulfonated polyethylene can form films with a high level of heat resistance, weather resistance, ozone resistance, chemical resistance, abrasion resistance, bending fatigue resistance and other properties, and is hence often used in the form of a latex for coating materials and adhesive materials. For example, a chlorosulfonated polyethylene latex is used as a latex component to form a resorcin-formalin-latex adhesive (hereinafter also referred to as an “RFL adhesive”), and timing belts for use in automobiles are produced using such a resorcin-formalin-latex adhesive, in which a matrix rubber, such as ethylene-propylene-diene rubber (EPDM) or hydrogenated acrylonitrile butadiene rubber (HNBR), and reinforcing fibers, such as polyamide resin fibers or glass fibers, are bonded together with the adhesive to form a composite with higher strength.
In view of standing stability or RFL adhesive strength, chlorosulfonated polyethylene latexes for use in RFL adhesives and the like have been usually prepared using a polyoxyethylene alkyl phenyl ether sulfate as an emulsifying agent (see, for example, Patent Literatures 1 and 2). However, latexes prepared using such an emulsifying agent raise the problem of retention of an alkyl phenol ether compound suspected of being an endocrine disruptor, and the use of such latexes are now being regulated for the safety of living bodies and the environment.
Other known examples of emulsifying agents for use in the production of chlorosulfonated polyethylene latexes include salts of fatty acids such as oleic acid and stearic acid, organic sulfates such as sodium lauryl sulfate and sodium higher alcohol sulfate, and organic sulfonates such as sodium dodecylbenzene sulfonate and sodium alkylnaphthalene sulfonate (see, for example, Patent Literature 3). However, chlorosulfonated polyethylene latexes prepared using these emulsifying agents are inferior in standing stability or mechanical stability to those prepared using a polyoxyethylene alkyl phenyl ether sulfate, and are also difficult to increase the adhesive strength of RFL adhesives even when used in RFL adhesives.